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Shading
In the remainder of the practical, we will consider the sensitivity of the results to the choice of inputs. This is a key part of model evaluation - how do the results change as the inputs change?
One key input for the model is the degree of shading of the canal by nearby buildings.
- What happens to the results if we exclude shading from the model?
- What happens to the results if we change the degree of shading?
While these questions are important for model evaluation, they also have important consequences for the management, development and governance of urban areas. This is of particular relevance for Manchester, which has a rapidly developing skyline (see the Guardian):
The transformation of the skyline over the last 15 years is quite remarkable:
With construction of new office and residential buildings on brownfield sites (previously developed for industrial or commercial purposes), and on sites close to the canal network, there is potential for increased shading of our waterways. How will this influence water temperature and the effects of the waterways on air temperature?
An exploration
To explore the effects of shading, we’ll focus on one single section of the Bridgewater Canal (bc_77).
This is a relatively large canal section, but there are few tall buildings in the surrounding area (Cornbrook) and as a result, minimal shading across the year. As a former industrial area, there is potential for new buildings and ‘regeneration’.
Inspect the canal and the nearby building geometries.
The plot below shows the modelled water temperature for bc_77, including the effects of shading.
Inspect the plot, which also includes the model with shading effects excluded (i.e., shading proportion = 0) and with full shading (i.e., shading proportion = 1).
How important is the current degree of shading by buildings in understanding change in water temperature through time?
How does water temperature change if the canal is fully shaded? When is this most important?
Air temperature
The above plot shows that water temperatures are influenced by the degree of shading, but how does this influence the effects of waterways on air temperatures?
This is illustrated in the plot below, where the 0 line (y axis) represents the modelled effects on air temperature when shading effects are excluded. This can then be compared to:
- a model incorproating the true shading of
bc_77[including_shading] - a model incorproating full shading (shading proportion = 1) [full_shading]
- a model where the shading proportion is based on a nearby section of the Rochdale Canal (
rc_9) [developed_shading]. This is closer to the city centre and is highly shaded by nearby buildings, so is used here as a proxy for the shading that could occur if this area was extensively developed.
Note: model results are presented relative to the the model excluding shading, where negative values denote relative cooling, and positive values denote relative warming.
How does adding shading (true / full / potential) influence the effect of the canal on air temperatures?
What is the magnitude of the potential change?